Method of Producing negative electrode for lithium secondary cell

ABSTRACT

A method of producing a negative electrode for a lithium secondary cell having thin films of lithium and a sulfide-based inorganic solid electrolyte is provided. In the method, are used a negative electrode base material and an inorganic solid electrolyte source material respectively placed in closed containers. The base material has a surface of lithium metal. The base material and the source material are respectively taken out from the closed containers in a chamber space, which is substantially inactive to lithium and which is insulated from air and provided adjacent to a thin film deposition system. The base material and the source material are transferred into the thin film deposition system without being exposed to the air. In system, the source material is used and a thin film of an inorganic solid electrolyte is formed on the base material. The base material having the thin film is transferred, without being exposed to the air, into a chamber space, which is substantially inactive to lithium. In chamber space, the base material having the thin film is placed into a closed container. Thus, a negative electrode can be produced without being degraded by air.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of producing a negativeelectrode for use in a lithium secondary cell.

[0003] 2. Description of the Background Art

[0004] A solid secondary cell with a thin lithium film has beenproposed. Japanese Patent Laying-Open No. 62-44960 discloses a methodfor manufacturing such a solid cell. The method includes successivelyforming a thin film of titanium disulfide as a positive electrode, athin film of Li₂O—Al₂O₃ as an electrolyte, and a thin film of Li as anegative electrode on a substrate placed in an ionized cluster beamevaporation system. Japanese Patent Publication No. 5-48582 discloses anelectrolytic material for such a solid cell.

[0005] On the other hand, advances have been made in commercializationof lithium secondary cells containing an organic solution ofelectrolytes. Lithium secondary cells are characterized by having ahigh-energy output per unit area or per unit weight as compared withother cells. Lithium secondary cells have been developed for practicaluse as a power source in mobile communications equipment, notebookcomputers, electric vehicles and the like.

[0006] An attempt has been made to use lithium metal for a negativeelectrode for the purpose of improving the performance of the lithiumsecondary cell containing an organic solution of electrolytes. Such anattempt, however, involves the risk of a dencdroid growth of the lithiummetal during charging and discharging. The dendroid growth may form aninternal short-circuit to a positive electrode and finally result in anexplosion. As a technique for avoiding the risk, an attempt can be madeto form a thin film of a sulfide-based inorganic solid electrolyte onthe lithium metal.

[0007] The lithium metal, the thin film of the sulfide-based inorganicsolid electrolyte, and the source materials therefor, however, arehighly reactive to water, so that they cause the problem of degradationwhen exposed to the air. The above-mentioned publications related to thesolid cell, however, do not suggest a technique for independentlyproducing a lithium-containing negative electrode itself. The problem ofthe degradation described above must be resolved for the production ofsuch a freestanding negative electrode containing lithium and thesulfide-based solid electrolyte.

SUMMARY OF THE INVENTION

[0008] An object of the present invention is to provide a method ofproducing a negative electrode for a lithium secondary cell, in whichlithium metal, a source material for a thin film of a sulfide-basedinorganic solid electrolyte, and a negative electrode having the thinfilm of the inorganic solid electrolyte formed thereon can be preventedfrom being degraded by

[0009] The present invention is directed to a method of producing anegative electrode for a lithium secondary cell having a thin film madeof an inorganic solid electrolyte. The method includes using a negativeelectrode base material placed in a closed container and an inorganicsolid electrolyte source material placed in a closed container. Thenegative electrode base material has a surface made of a materialselected from the group consisting of lithium metal and lithium alloys.In the method, the negative electrode base material placed in the closedcontainer and the inorganic solid electrolyte source material placed inthe closed container are placed into a chamber space, which issubstantially inactive to lithium and which is insulated from air andprovided adjacent to an apparatus for forming a thin film. In thechamber space, the negative electrode base material and the sourcematerial are respectively taken out from the closed containers. Then,the negative electrode base material and the source material taken outare transferred into the apparatus for forming a thin film without beingexposed to the air. In the apparatus, the materials are used, and a thinfilm made of an inorganic solid electrolyte is formed on the negativeelectrode base material. The negative electrode base material having thethin film formed thereon is then transferred without being exposed tothe air into a chamber space, which is substantially inactive to lithiumand which is insulated from the air and provided adjacent to theapparatus. In the chamber space, the negative electrode base materialhaving the thin film is placed into a closed container. The negativeelectrode having the thin film placed in the closed container can betaken out from the chamber into the air without being degraded.

[0010] The negative electrode base material for use in the method may beprepared by forming a thin film made of a material selected from thegroup consisting of lithium metal and lithium alloys on a base materialby vapor deposition. The thin film made of the material selected fromthe group consisting of lithium metal and lithium alloys preferably hasa thickness of 20 μm or less. The thickness of the thin film istypically in the range of 0.1 μm to 20 μm, and preferably in the rangeof 1 μm to 10 μm.

[0011] The present invention is directed to another method of producinga negative electrode for a lithium secondary cell having a thin filmmade of an inorganic solid electrolyte. The method includes using afirst source material placed in a closed container and a second sourcematerial placed in a closed container. The first source material isselected from the group consisting of lithium metal and lithium alloys.The second source material is for use in forming the inorganic solidelectrolyte. The first and second source materials respectively placedin the closed containers are placed into a chamber space, which issubstantially inactive to lithium and which is insulated from air andprovided adjacent to an apparatus for forming a thin film. In thechamber space, the first and second source materials are respectivelytaken out from the closed containers. Then, the first and second sourcematerials taken out are transferred into the apparatus without beingexposed to the air. In the apparatus, the first and second materials areused, and a first thin film made of the first source material and asecond thin film made of the second source material are formed on a basematerial. The base material having the first and second thin filmsformed thereon is then transferred without being exposed to the air intoa chamber space, which is substantially inactive to lithium and which isinsulated from the air and provided adjacent to the apparatus. In thechamber space, the base material having the first and second thin filmsis placed into a closed container. The negative electrode having thethin films placed in the closed container can be taken out from thechamber into the air without being degraded.

[0012] In the method, the first thin film may be formed by a vapordeposition method. The first thin film preferably has a thickness of 20μm or less. The thickness of the thin film formed is typically in therange of 0.1 m to 20 μm, and preferably in the range of 1 μm to 10 μm.

[0013] The present invention is directed to a further method ofproducing a negative electrode for a lithium secondary cell having athin film made of an inorganic solid electrolyte. In the method, a firstsource material selected from the group consisting of lithium metal andlithium alloys is placed in a closed container, and the first sourcematerial placed in the container is placed into a chamber space, whichis substantially inactive to lithium and which is insulated from air andprovided adjacent to a first apparatus for forming a thin film. In thechamber space, the first source material is taken out from the closedcontainer. Then, the first source material taken out is transferred intothe first apparatus without being exposed to the air. In the firstapparatus, the first source material is used, and a first thin film madeof the first source material is formed on a base material. The basematerial having the first thin film formed thereon is transferred fromthe first apparatus without being exposed to the air into a chamberspace, which is substantially inactive to lithium and which is insulatedfrom the air and provided adjacent to the first apparatus. In thechamber space, the base material having the first thin film formedthereon is placed into a closed container. Then, the base materialhaving the first thin film formed thereon and being placed in the closedcontainer, and a second source material for forming an inorganic solidelectrolyte and being placed in a closed container are placed into achamber space, which is substantially inactive to lithium and which isinsulated from the air and provided adjacent to a second apparatus forforming a thin film. In the chamber space, the base material having thefirst thin film formed thereon and the second source material arerespectively taken out from the closed containers. Then, the basematerial having the first thin film formed thereon and the second sourcematerial taken out are transferred into the second apparatus withoutbeing exposed to the air. In the second apparatus, the second sourcematerial is used, and a second thin film made of the second sourcematerial is formed on the first thin film. The base material having thefirst and second thin films formed thereon is transferred from thesecond apparatus without being exposed to the air into a chamber space,which is substantially inactive to lithium and which is insulated fromthe air and provided adjacent to the second apparatus. In the chamberspace, the base material is placed into a closed container.

[0014] In the method, the first thin film may be formed by a vapordeposition method. The first thin film preferably has a thickness of 20μm or less. The thickness of the thin film formed is typically in therange of 0.1 μm to 20 μm, and preferably in the range of 1 μm to 10 μm.

[0015] As described above, the source materials, the base materials, andthe base materials having the thin film can be handled without beingexposed to air, so that a negative electrode for a lithium secondarycell can be prepared without being degraded by air.

[0016] In the above-described methods, when the source material is takenout and transferred into the apparatus, the chamber space and theapparatus are preferably filled with a gas selected from the groupconsisting of helium, nitrogen, neon, argon, krypton, a mixture gas oftwo or more from the foregoing, and dry air having a dew point of −50°C. or below. When the base material having the thin film formed thereonis taken out from the apparatus and transferred into the chamber spaceto be placed into the closed container, the chamber space and theapparatus are also preferably filled with a gas selected from the groupconsisting of helium, nitrogen, neon, argon, krypton, a mixture gas oftwo or more from the foregoing, and dry air having a dew point of −50°C. or below.

[0017] The inorganic solid electrolytes may include sulfides, oxides,nitrides, and mixtures thereof such as oxynitrides and oxysulfides. Thesulfides may include Li₂S, a compound of Li₂S and SiS₂, a compound ofLi₂S and GeS₂, and a compound of Li₂S and Ga₂S₃. The oxynitrides mayinclude Li₃PO_(4-x)N_(2x/3), Li₄SiO_(4-x)N_(2x/3),Li₄Geo_(4-x)N_(2x/3)(0<x<4), and Li₃BO_(3-x)N_(2x/3), (0<x<3).

[0018] In the present invention, the thin film made of the inorganicsolid electrolyte specifically contains components A to C as follows:

[0019] A: lithium, the content of which is in the range of 30% to 65% byatomic percent;

[0020] B: one or more elements selected from the group consisting ofphosphorus, silicon, boron, germanium, and gallium; and

[0021] C: sulfur.

[0022] The thin film made of the inorganic solid electrolyte may furthercontain at least one of oxygen and nitrogen. The content of element B istypically 0.1% to 30% by atomic percent. The content of element C istypically 20% to 60% by atomic percent. The content of one or both ofoxygen and nitrogen is typically 0.1% to 10%.

[0023] In the present invention, the thin film made of the inorganicsolid electrolyte may be amorphous. The thin film made of the inorganicsolid electrolyte preferably has an ionic conductance (conductivity) ofat least 1×10⁻⁴ S/cm at 25° C. The ionic conductance of the thin film ofthe inorganic solid electrolyte at 25° C. may be typically in the rangeof 1×10⁻⁴ S/cm to 2.5×10⁻³ S/cm, and preferably in the range of 5×10⁻⁴S/cm to 2.5×10⁻³ S/cm. The thin film of the inorganic solid electrolyteformed in the present invention may have an activation energy of 40kJ/mol or below. The activation energy of the thin film of the inorganicsolid electrolyte may be in the range of 30 kJ/mol to 40 kJ/mol.

[0024] In the present invention, the thin film made of the inorganicsolid electrolyte may be formed by a vapor deposition method, andtypically, is formed by any one method selected from the groupconsisting of sputtering, vapor evaporation, laser ablation, and ionplating. In the present invention, the thin film made of lithium metalor a lithium alloy may also be formed by a vapor deposition method, andtypically, is formed by any one method selected from the groupconsisting of sputtering, vapor evaporation, laser ablation, and ionplating.

[0025] The negative electrode produced by the present invention may beused to form a lithium secondary cell together with other necessarycomponents such as a separator of porous polymer, a positive electrode,and an organic solution of electrolytes.

[0026] According to the present invention, the thin film made of theorganic solid electrolyte is formed on the base material having asurface made of lithium metal or a lithium alloy, or the thin film madeof lithium metal or a lithium alloy is formed on the negative electrodebase material and then the thin film made of the inorganic solidelectrolyte is formed thereon. The additive elements of the lithiumalloys may include In, Ti, Zn, Bi, and Sn.

[0027] The base material having a surface made of lithium or a lithiumalloy may be composed of a base material made of a metal or an alloy anda thin film made of lithium or a lithium alloy formed thereon.Specifically, the base material may be composed of a metal material(typically a metal foil or leaf) of at least one selected from the groupconsisting of copper, nickel, aluminum, iron, niobium, titanium,tungsten, indium, molybdenum, magnesium, gold, silver, platinum, alloysof two or more metals from the foregoing, and stainless steel, and athin film made of lithium or a lithium alloy formed on the metalmaterial. Alternatively, the base material for use in the process may becomposed of a metal oxide such as SnO₂ or an electrically conductivecarbon such as graphite, and a thin film made of lithium or a lithiumalloy formed thereon. In the above-described base materials, the thinfilm made of lithium or a lithium alloy typically has a thickness of 0.1μm to 20 μm, and preferably a thickness of 1 μm to 10 μm. On the otherhand, a foil or leaf made of lithium or a lithium alloy may be used asthe base material. The base material used in the present invention mayhave a thickness of 1 μm to 100 μm from the viewpoint of application tothe lithium cell and may have a thickness of 1 μm to 20 μm to give acompact product.

[0028] In the present invention, the negative electrode base materialfor use in depositing the thin lithium metal or lithium alloy film maybe made of a metal, an alloy, a metal oxide such as SnO₂, anelectrically conductive carbon such as graphite, or the like. The metaland the alloy used for the base material may include at least one ofcopper, nickel, aluminum, iron, niobium, titanium, tungsten, indium,molybdenum, magnesium, gold, silver, platinum, or an alloy of two ormore metals from the foregoing, or stainless steel. The negativeelectrode base material preferably has a thickness of not more than 100μm in order to reduce the size of the lithium cell, and preferably has athickness of not less than 1 μm in order to keep an enough strength ofthe base material. Therefore, the thickness of the negative electrodebase material may be 1 μm to 100 μm, and may be 1 μm to 20 μm forcompactness.

[0029] In the step of forming the thin film made of the inorganic solidelectrolyte, the thin film made of the inorganic solid electrolyte maybe formed on a heated base material by a vapor deposition method, or thethin film made of the inorganic solid electrolyte may be formed on abase material at room temperature or at a temperature below 40° C. andthen the thin film made of the inorganic solid electrolyte may besubjected to heat treatment. Such heat treatment allows the thin film tohave a relatively high ionic conductance. Generally, a heater may beused for the heat treatment. The heater employed may be attached to aholder for holding the base material or may be a radiation heater. Theheater heats the base material or the thin film formed on the basematerial. On the other hand, the heating may be effected through atemperature rise caused by plasma or the like during the filmdeposition. In the film deposition process, plasma or the like can heatthe base material, so that the thin film can be formed on the basematerial having a increased temperature. The heat treatment caneffectively be carried out at a temperature higher than room temperature(5° C. to 35° C.) or at a temperature of 40° C. or higher. Thus, atemperature higher than room temperature such as a temperature of 40° C.or higher, preferably 100° C. or higher may be used as the base materialtemperature in the case that the thin film is heated through the heatingof the base material, or as the temperature for the heat treatment ofthe formed thin film. The thin film of the inorganic solid electrolyteis generally amorphous, and specifically glassy. Therefore, when theheating temperature is too high and close to the glass transitiontemperature of the thin film of the inorganic solid electrolyte, theamorphous structure of the obtained thin film may be degraded, and itsionic conductance may be lowered. Thus, the heating temperature ispreferably below the glass transition temperature of the thin film ofthe inorganic solid electrolyte. Based on this point, a temperature of200° C. or below is preferably used as the temperature of the substratein the case that the thin film is heated through the heating of thesubstrate, or as the temperature for the heat treatment of the formedthin film. In addition, when the thin film of the inorganic solidelectrolyte is formed on lithium metal, the heating temperature ispreferably lower than 179° C. which is the melting point of metallithium. Thus, the heating temperature is preferably lower than atemperature at which the texture of the thin film of the inorganic solidelectrolyte changes (for instance, the glass transition temperature ofthe thin film of the inorganic solid electrolyte) and lower than atemperature at which the structure of the base material can no longer bemaintained (for instance, the melting point of the base material).Specifically, the heating temperature is preferably 40° C. to 200° C.,and more preferably not lower than 100° C. and lower than 179° C.

[0030] The thin film of the inorganic solid electrolyte formed in thepresent invention typically has a thickness of 0.01 μm to 10 μm, andpreferably a thickness of 0.1 μm to 2 μm.

[0031] In the present invention, the degree of vacuum of the backgroundin the vapor deposition method is preferably not higher than 1.33×10⁻⁴Pa (1×10⁻⁶ Torr). When the thin film of the inorganic solid electrolyteis formed on lithium metal or a lithium alloy, a low vacuum degree mayinduce oxidation or degradation of the lithium by water. The atmosphereunder which the thin film is formed by the vapor deposition method maycomprise a gas inactive to lithium, such as helium, neon, argon,krypton, or a mixture gas of two or more from the foregoing. The purityof the gas constituting the atmosphere is preferably at least 99.99% sothat no degradation of the lithium due to the water may occur when thethin film of the inorganic solid electrolyte is formed on lithium metalor a lithium alloy.

[0032] The foregoing and other objects, features, aspects and advantagesof the present invention will become more apparent from the followingdetailed description of the present invention when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a schematic diagram showing the entire formation of anapparatus used for the present invention.

[0034] In the drawing, a thin film deposition system is denoted by areference numeral 1, an inlet of the thin film deposition system by 2,an outlet of the thin film deposition system by 3, and chambers by 4 and5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1

[0035] A copper foil or leaf having a size of 100 mm×50 mm and athickness of 10 μm was bonded to a lithium metal foil or leaf having thesame size and a thickness of 50 μm to produce a negative electrode basematerial. On the lithium metal foil or leaf of the produced basematerial, a thin film of an inorganic solid electrolyte having athickness of 1 μm was formed by the sputtering of a Li₂S—SiS₂—P₂O₅-basedtarget at room temperature under an Ar gas atmosphere to produce anegative electrode.

[0036] As described below, the negative electrode base material and theLi₂S—SiS₂—P₂O₅-based target is placed into a thin film deposition systemand the negative electrode having the thin film of the inorganic solidelectrolyte is taken out. FIG. 1 shows the entire formation of theapparatus used for the production of the negative electrode. First, thenegative electrode base material and the target contained in a closedcontainer of glass, plastic or the like is introduced into a chamber 4attached to an inlet 2 of a thin film deposition system 1, and then, airis evacuated from chamber 4. Then, chamber 4 is filled with argon gashaving a purity of 99.99%. Thin film deposition system 1 is also filledwith argon gas of 99.99% purity. Gloves are attached to chamber 4 sothat one may insert the hands into the gloves to perform operationswithin chamber 4. The closed container is opened in chamber 4, and thenegative electrode base material having the lithium metal foil or leafand the target are taken out. Then, a door at inlet 2 of the thin filmdeposition system is opened, the negative electrode base material andthe target are placed into thin film deposition system 1, and the doorat inlet 2 is closed. In this manner, the negative electrode basematerial and the target are placed into thin film deposition system 1without being exposed to air.

[0037] In thin film deposition system 1, the target is used and the thinfilm of the inorganic solid electrolyte is formed on the negativeelectrode base material by the sputtering to produce a negativeelectrode. Then, thin film deposition system 1 is filled with argon gashaving a purity of 99.99%. Then, air is evacuated from a chamber 5attached to an outlet 3 of thin film deposition system 1, andthereafter, chamber 5 is filled with argon gas of 99.99% purity. Likechamber 4, chamber 5 also has gloves so that one may insert the handsinto the gloves to perform operations within chamber 5. A door at outlet3 of the thin film deposition system is opened, the negative electrodehaving the thin film of the inorganic solid electrolyte is taken outfrom thin film deposition system 1 and is placed into chamber 5, and thedoor at outlet 3 is closed. A closed container of glass, plastic or thelike was placed into chamber 5 in advance. The negative electrode havingthe thin film of the inorganic solid electrolyte is placed into thecontainer and the container is closed, and the closed container is takenout into the air. In this manner, the negative electrode having the thinfilm of the inorganic solid electrolyte can be transferred from thinfilm deposition system 1 to another place without being exposed to theair.

[0038] In this process, any one of helium, nitrogen, neon, argon, andkrypton, or a mixture gas of two or more from the foregoing, or dry airhaving a dew point of −50° C. or below can be used without a problem.The gases used in the respective chambers and the thin film depositionsystem may be the same or different as required.

[0039] The apparatus as shown in FIG. 1 has both of inlet 2 and outlet 3for the thin film deposition system. Alternatively, one passage maydouble as the inlet and the outlet, and one chamber may be providedthough which the base member and the source material are introduced intothe thin film deposition system and the negative electrode is taken outfrom the thin film deposition system.

[0040] An X-ray diffraction analysis revealed that the formed thin filmof the inorganic solid electrolyte was in an amorphous state. The ionicconductance of the thin film of the inorganic solid electrolyte was3×10⁻⁴ S/cm at 25° C. A composition analysis revealed that the thin filmhad a composition of Li (0.42): Si (0.13): S (0.44): P (0.002): O(0.008) by atomic ratio.

[0041] A mixture solution of ethylene carbonate (EC) and propylenecarbonate (PC) was heated, and then LiPF₆ was dissolved in the solution.Polyacrylonitrile (PAN) was dissolved in the mixture solution in a highconcentration. The solution was cooled to give a PAN preparationcontaining large amounts of EC and PC with LiPF₆ dissolved. LiCoO₂particles as an active material and carbon particles for providingelectron conductivity were added to the PAN preparation. The resultingmixture was applied in a thickness of 300 μm onto a 20 μm-thick aluminumfoil or leaf (a collector member for a positive electrode) to produce apositive electrode.

[0042] The negative electrode having the thin film of the solidelectrolyte, a separator (porous polymer film) and the positiveelectrode were stacked and then placed into a stainless steel containerto be sealed. An organic solution of an electrolyte containing 1 mole %LiPF₆ as the electrolytic salt in a mixture solution of ethylenecarbonate and propylene carbonate was added dropwise to the container.In such a process, a lithium secondary cell was prepared under an argongas atmosphere having a dew point of −60° C. or below.

[0043] The prepared cell was examined for the charge and dischargecharacteristics. In the examination, the cell was charged at a voltageof 4.2 V and maintained a capacity of 0.5 Ah (ampere-hour) until aconstant discharge at 100 mA allowed the voltage to drop to 3.5 V. Theenergy density of the cell was 490 Wh (watt-hour)/l (iter). The cellalso remained stable after one hundred cycles of charge and dischargeunder the same conditions.

Example 2

[0044] Except that the thin film of the inorganic solid electrolyte wasformed by vacuum evaporation, a negative electrode and a lithiumsecondary cell were produced and evaluated as in Example 1. The obtainedresults were the same as those in Example 1.

Example 3

[0045] Except that the thin film of the inorganic solid electrolyte wasformed by laser ablation, a negative electrode and a lithium secondarycell were produced and evaluated as in Example 1. The composition of theformed thin film was found to be Li (0.40): Si (0.13): S (0.46): P(0.003): O (0.007) by atomic ratio. Except for the composition, theobtained results were the same as those in Example 1.

Example 4

[0046] Except that the thin film of the inorganic solid electrolyte wasformed by ion plating, a negative electrode and a lithium secondary cellwere produced and evaluated as in Example 1. The obtained results werethe same as those in Example 1.

Example 5

[0047] A copper foil or leaf having a size of 100 mm×50 mm and athickness of 10 μm was placed in a thin film deposition system. On thecopper foil or leaf, a thin film of lithium metal having a thickness of5 μm was formed by the sputtering of a lithium metal target, andthereon, a thin film of an inorganic solid electrolyte having athickness of 1 μm was formed by the sputtering of a Li₂S—SiS₂—P₂O₅-basedtarget. The sputtering was carried out at room temperature under an Argas atmosphere. As in the case of Example 1, the lithium metal targetand the Li₂S—SiS₂—P₂O₅-based target were introduced into a thin filmdeposition system and the negative electrode having the thin films oflithium metal and the inorganic solid electrolyte were taken out. Theapparatus as shown in FIG. 1 was used to produce a negative electrode.After the copper foil or leaf was placed into thin film depositionsystem 1, closed containers of glass, plastic or the like respectivelycontaining the two targets were placed into chamber 4 attached to inlet2 of thin film deposition system 1, and then, air was evacuated fromchamber 4. Then, chamber 4 was filled with argon gas having a purity of99.99%. Thin film deposition system 1 was also filled with argon gas of99.99% purity. By the hands inserted into the gloves attached to chamber4, the closed containers were opened in chamber 4 and the two targetswere respectively taken out from the closed containers. Then, a door atinlet 2 of the thin film deposition system was opened, the two targetswere placed into thin film deposition system 1, and the door at inlet 2was closed. In this manner, the two targets were placed into thin filmdeposition system 1 without being exposed to the air. In thin filmdeposition system 1, a lithium metal thin film was formed on the copperfoil or leaf by the sputtering of the lithium metal target, and thereon,a thin film of an inorganic solid electrolyte was formed by thesputtering of the Li₂S—SiS₂—P₂O₅-based target. Thereafter, air wasevacuated from chamber 5 attached to outlet 3 of thin film depositionsystem 1 filled with argon gas of 99.99% purity. Chamber 5 was thenfilled with argon gas of 99.99% purity. By the hands inserted into thegloves attached to chamber 5, a door at outlet 3 of the thin filmdeposition system was opened, the negative electrode having the twokinds of thin films was taken out from thin film deposition system 1 andthen placed into chamber 5, and the door at outlet 3 was closed. Aclosed container of glass, plastic or the like was provided in chamber 5in advance, and the negative electrode having the thin films was placedinto the container. The container was closed, and the closed containerwas taken out into the air.

[0048] The obtained negative electrode was examined as in the case ofExample 1. The obtained results were the same as those in Example 1.

Example 6

[0049] Except that the thin film of lithium metal and the thin film ofthe inorganic solid electrolyte were formed by vacuum evaporation, anegative electrode and a lithium secondary cell were produced andevaluated as in Example 4. The obtained results were the same as thosein Example 1.

Example 7

[0050] Except that the thin film of lithium metal and the thin film ofthe inorganic solid electrolyte were formed by laser ablation, anegative electrode and a lithium secondary were produced and evaluatedas in Example 5. The obtained results were the same as those in Example4.

Example 8

[0051] Except that the thin film of the inorganic solid electrolyte wasformed by ion plating, a negative electrode and a lithium secondary cellwere produced and evaluated as in Example 1. The obtained results werethe same as those in Example 1.

Example 9

[0052] Except that Li₂S—SiS₂—Li₂O—P₂O₅ was used to form the thin film ofthe inorganic solid electrolyte, a negative electrode and a secondarycell were produced and evaluated as in Example 1. The composition of thethin film was Li (0.43): Si (0.12): S (0.44): P (0.002): O (0.008) byatomic ratio. Except for the composition, the obtained results were thesame as those in Example 1.

Example 10

[0053] Except that the thin film of the inorganic solid electrolyte wasformed by vacuum evaporation, a negative electrode and a lithiumsecondary cell were produced and evaluated as in Example 9. The obtainedresults were the same as those in Example 9.

Example 11

[0054] Except that the thin film of the inorganic solid electrolyte wasformed by laser ablation, a negative electrode and a lithium secondarycell were produced and evaluated as in Example 9. As a result, thecomposition of the thin film was found to be Li (0.41): Si (0.13): S(0.45): P (0.002): O (0.008) by atomic ratio. Except for thecomposition, the obtained results were the same as those in Example 9.

Example 12

[0055] Except that the thin film of the inorganic solid electrolyte wasformed by ion plating, a negative electrode and a lithium secondary cellwere produced and evaluated as in Example 9. The obtained results werethe same as those in Example 9.

Example 13

[0056] Except that Li₂S—SiS₂—Li₂O—P₂O₅ was used to form the thin film ofthe inorganic solid electrolyte and the thin film of lithium metal wasformed by vacuum evaporation, a negative electrode and a lithiumsecondary cell were produced and evaluated as in Example 9. The obtainedresults were the same as those in Example 9.

Example 14

[0057] Except that the thin film of the inorganic solid electrolyte wasformed by vacuum evaporation, a negative electrode and a lithiumsecondary cell were produced and evaluated as in Example 13. Theobtained results were the same as those in Example 9.

Example 15

[0058] Except that the thin film of the inorganic solid electrolyte wasformed by laser ablation, a negative electrode and a lithium secondarycell were produced and evaluated as in Example 13. The obtained resultswere the same as those in Example 11.

Example 16

[0059] Except that the thin film of the inorganic solid electrolyte wasformed by ion plating, a negative electrode and a lithium secondary cellwere produced and evaluated as in Example 13. The obtained results werethe same as those in Example 9.

Example 17

[0060] A lithium metal thin film having a thickness of 10 μm was formedon a copper foil or leaf having a size of 100 mm×50 mm and a thicknessof 10 μm by vacuum evaporation. On the thin film of lithium metal, athin film of an inorganic solid electrolyte was formed to have athickness of 1 μm. On the other hand, two lithium metal foils or leafseach having the same size as the copper foil or leaf and each having athickness of 30 μm were bonded to each other. The bonded lithium foilsor leafs were used in place of the copper foil or leaf. The thin film ofthe inorganic solid electrolyte could be formed in a similar manner onthe bonded lithium metal foils or leafs. As in the case of Example 1,the lithium metal target and the electrolyte target were placed into thethin film deposition system and the negative electrode having thelithium metal thin film and the thin film of the inorganic solidelectrolyte were taken out. The apparatus as shown in FIG. 1 was used toproduce the negative electrode. The conditions as shown in Tables 1 to 5were used to form thin films of inorganic solid electrolytes. Tables 1to 5 also show the ionic conductance at 25° C. of the thin films of theinorganic solid electrolytes, and the activation energy of the thin filmof the inorganic solid electrolytes. The activation energy was obtainedby the measurement of the temperature dependency of the ionicconductance at raised temperatures. TABLE 1 Method of Temperature ofheat Ionic Activation Sample film Inorganic solid Film depositiontreatment after film conductance energy No. deposition electrolytematerial temperature (° C.) deposition (° C.) (S/cm) (kJ/mol) 1Sputtering 57Li₂S—38SiS₂—5(Li₂O—P₂O₅)  50 No heat treatment 7.0 × 10⁻⁴36 2 Sputtering 57Li₂S—38SiS₂—5(Li₂O—P₂O₅) 100 No heat treatment 1.8 ×10⁻³ 32 3 Sputtering 57Li₂S—38SiS₂—5(Li₂O—P₂O₅) 130 No heat treatment2.0 × 10⁻³ 32 4 Sputtering 57Li₂S—38SiS₂—5(Li₂O—P₂O₅) Room temperature(25° C.)  50 6.0 × 10⁻⁴ 37 5 Sputtering 57Li₂S—38SiS₂—5(Li₂O—P₂O₅) Roomtemperature (25° C.) 100 1.6 × 10⁻³ 33 6 Sputtering57Li₂S—38SiS₂—5(Li₂O—P₂O₅) Room temperature (25° C.) 130 1.7 × 10⁻³ 32 7Sputtering 60Li₂S—40SiS₂ 100 No heat treatment 1.5 × 10⁻³ 34 8Sputtering 60Li₂S—40SiS₂ 150 No heat treatment 1.5 × 10⁻³ 33

[0061] TABLE 2 Method of Temperature of heat Ionic Activation Samplefilm Inorganic solid Film deposition treatment after film conductanceenergy No. deposition electrolyte material temperature (° C.) deposition(° C.) (S/cm) (kJ/mol) 9 Sputtering 60Li₂S—40SiS₂ Room temperature (25°C.) 150 1.5 × 10⁻³ 32 10 Sputtering 57Li₂S—38SiS₂—5Li₃PO₄ 130 No heattreatment 1.7 × 10⁻³ 34 11 Sputtering 59.5Li₂S—40SiS₂—0.5Li₃PO₄ 130 Noheat treatment 1.6 × 10⁻³ 34 12 Sputtering 57Li₂S—38SiS₂—5Li₄SiO₄ 130 Noheat treatment 1.8 × 10⁻³ 33 13 Sputtering57Li₂S—38SiS₂—5Li₃PO_(3.9)N_(0.1) 130 No heat treatment 1.8 × 10⁻³ 34 14Sputtering 65Li₂S—34.5SiS₂—0.5Li₃PO₄ 130 No heat treatment 1.7 × 10⁻³ 3415 Laser ablation 60Li₂S—40SiS₂ 120 No heat treatment 1.9 × 10⁻³ 33 16Laser ablation 57Li₂S—38SiS₂—5(Li₂O—P₂O₅) 120 No heat treatment 2.0 ×10⁻³ 32 17 Laser ablation 57Li₂S—38SiS₂—5Li₃PO₄ 120 No heat treatment2.0 × 10⁻³ 33 18 Laser ablation 57Li₂S—38SiS₂—5Li₄SiO₄ 120 No heattreatment 2.1 × 10⁻³ 34

[0062] TABLE 3 Method of Temperature of heat Ionic Activation Samplefilm Inorganic solid Film deposition treatment after film conductanceenergy No. deposition electrolyte material temperature (° C.) deposition(° C.) (S/cm) (kJ/mol) 19 Laser ablation 60Li₂S—40SiS₂ Room temperature(25° C.) 140 1.7 × 10⁻³ 33 20 Laser ablation 57Li₂S—38SiS₂—5(Li₂O—P₂O₅)Room temperature (25° C.) 140 2.0 × 10⁻³ 32 21 Laser ablation57Li₂S—38SiS₂—5Li₃PO₄ Room temperature (25° C.) 140 1.8 × 10⁻³ 34 22Laser ablation 57Li₂S—38SiS₂—5Li₄SiO₄ Room temperature (25° C.) 140 1.7× 10⁻³ 34 23 Vacuum evaporation 60Li₂S—40SiS₂ 120 No heat treatment 1.7× 10⁻³ 33 24 Vacuum evaporation 60Li₂S—40SiS₂ 150 No heat treatment 1.8× 10⁻³ 32 25 Vacuum evaporation 57Li₂S—38SiS₂—5Li₃PO₄ 100 No heattreatment 1.8 × 10⁻³ 33 26 Vacuum evaporation 57Li₂S—38SiS₂—5Li₃PO₄ 120No heat treatment 2.0 × 10⁻³ 32 27 Vacuum evaporation57Li₂S—38SiS₂—5Li₃PO₄ 160 No heat treatment 2.1 × 10⁻³ 31

[0063] TABLE 4 Method of Temperature of heat Ionic Activation SampleFilm Inorganic solid Film deposition treatment after film conductanceenergy No. deposition electrolyte material temperature (° C.) deposition(° C.) (S/cm) (kJ/mol) 28 Vacuum evaporation 60Li₂S—39.5SiS₂—0.5Li₃PO₄120 No heat treatment 1.8 × 10⁻³ 33 29 Vacuum evaporation57Li₂S—38SiS₂—5(Li₂O—P₂O₅) 120 No heat treatment 2.0 × 10⁻³ 32 30 Vacuumevaporation 57Li₂S—38SiS₂—5Li₄SiO₄ 120 No heat treatment 2.0 × 10⁻³ 3431 Vacuum evaporation 60Li₂S—39.5SiS₂—0.5Li₄SiO₄ 120 No heat treatment2.1 × 10⁻³ 33 32 Vacuum evaporation 57Li₂S—38SiS₂—5Li₃BO₃ 120 No heattreatment 1.8 × 10⁻³ 34 33 Vacuum evaporation 57Li₂S—38SiS₂—5Li₄GeO₄ 120No heat treatment 1.7 × 10⁻³ 33 34 Vacuum evaporation60Li₂S—39.5GeS₂—0.5Li₄SiO₄ 120 No heat treatment 1.5 × 10⁻³ 33 35 Vacuumevaporation 60Li₂S—39.5Ga₂S₃—0.5Li₄SiO₄ 120 No heat treatment 1.8 × 10⁻³32 36 Vacuum evaporation 60Li₂S—39.5P₂S₅—0.5Li₄SiO₄ 120 No heattreatment 1.7 × 10⁻³ 34 37 Vacuum evaporation 57Li₂S—38SiS₂—5Li₃PO₄ Roomtemperature (25° C.) 120 1.9 × 10⁻³ 34

[0064] TABLE 5 Method of Temperature of heat Ionic Activation Samplefilm Inorganic solid Film deposition treatment after film conductanceenergy No. deposition electrolyte material temperature (° C.) deposition(° C.) (S/cm) (kJ/mol) 38 Vacuum evaporation 57Li₂S—38SiS₂—5Li₄SiO₄ Roomtemperature (25° C.) 160 1.8 × 10⁻³ 33 39 Vacuum evaporation60Li₂S—40SiS₂ Room temperature (25° C.) 120 1.7 × 10⁻³ 32 40 Vacuumevaporation 57Li₂S—38SiS₂—5Li₃PO_(3.9)N_(0.1) 120 No heat treatment 1.9× 10⁻³ 33 41 Vacuum evaporation 60Li₂S—39.5SiS₂—0.5Li₃PO₄ 120 No heattreatment 2.0 × 10⁻³ 32 42 Vacuum evaporation 65Li₂S—34.5SiS₂—0.5Li₃PO₄130 No heat treatment 1.9 × 10⁻³ 34 43 Vacuum evaporation55Li₂S—44.5SiS₂—0.5Li₃PO₄ 130 No heat treatment 1.8 × 10⁻³ 33 44 Ionplating 57Li₂S—38SiS₂—5Li₃PO₄ 120 No heat treatment 1.8 × 10⁻³ 33 45 Ionplating 60Li₂S—39.5SiS₂—0.5Li₃PO₄ 120 No heat treatment 2.0 × 10⁻³ 32 46Ion plating 57Li₂S—38SiS₂—5Li₃PO₄ Room temperature (25° C.) 120 1.7 ×10⁻³ 34 47 Ion plating 60Li₂S—39.5SiS₂—0.5Li₃PO₄ Room temperature (25°C.) 120 1.9 × 10⁻³ 32

[0065] Each base material having the thin film of lithium metal and thethin film of the inorganic solid electrolyte formed thereon was used asa negative electrode to produce a lithium secondary cell. Each negativeelectrode, a separator of porous polymer film, a positive electrode, anorganic solution of electrolytes, and other conventionally requiredcomponents were assembled into a lithium secondary cell. The outline ofthe process of the cell and the results of examining the cell are asfollows.

[0066] A mixture solution of ethylene carbonate (EC) and propylenecarbonate (PC) was heated, and then LiPF₆ was dissolved in the solution.Polyacrylonitrile (PAN) was dissolved in the mixture solution in a highconcentration. The solution was cooled to give a PAN preparationcontaining large amounts of EC and PC with LiPF₆ dissolved. LiCoO₂particles as an active material and carbon particles for providingelectron conductivity were added to the PAN preparation. The resultingmixture was applied in a thickness of 300 μm onto a 20 μm-thick aluminumfoil or leaf (a collector member for a positive electrode) to produce apositive electrode.

[0067] Each negative electrode having the thin film of the solidelectrolyte, a separator (porous polymer film), and the positiveelectrode were stacked and then placed into a stainless steel container.An organic solution of an electrolyte containing 1 mole % LiPF₆ as theelectrolytic salt in a mixture solution EC and PC was added dropwise tothe container. The stainless steel container was sealed under an argongas atmosphere having a dew point of −60° C. or below to give a lithiumsecondary cell.

[0068] The prepared cells were examined for the charge and dischargecharacteristics. In the examination, each cell was charged at a voltageof 4.2 V and maintained a capacity of 0.5 Ah (ampere-hour) until aconstant discharge at 100 mA allowed the voltage to drop to 3.5 V. Theenergy density of each cell was in the range of 500 to 550 Wh(watt-hour)/l (liter). Each cell also remained stable after one hundredcycles of charge and discharge under the same conditions.

[0069] In Examples 5 to 8 and 13 to 16, the thin lithium metal film andthe thin film of the inorganic solid electrolyte may be formed by thesame method, or by different methods. In the latter case, an apparatusavailable for two or more kinds of thin film deposition methods may beused, and for example, the thin lithium metal film may be formed byvacuum evaporation and the thin film of the inorganic solid electrolyteby sputtering.

[0070] In Examples 5 to 8, the thin lithium metal film and the thin filmof the inorganic solid electrolyte were formed in the same apparatus.Alternatively, first, the thin lithium metal film may only be formed,and then, the thin film of the inorganic solid electrolyte may be formedon the lithium film by a similar process in another apparatus.Specifically, the following process may be employed. The thin lithiummetal film is formed on the base member by a process similar to that inthe Examples, and the product may be placed into a closed containerwithout being exposed to the air. By a process similar to that in theExamples, the base member having the thin lithium metal film is takenout from the closed container into another apparatus without beingexposed to the air. The thin film of the inorganic solid electrolyte isformed in the different apparatus. In a similar manner, the obtainednegative electrode is placed into a closed container without beingexposed to the air.

[0071] Instead of the lithium metal, lithium alloys may be used. Theadditive elements that can constitute the lithium alloys may include In,Ti, Zn, Bi, and Sn. The lithium alloys may be deposited on the basematerial by a common vapor deposition method such as sputtering, vacuumevaporation, or laser ablation.

[0072] As seen from the above, the negative electrode produced accordingto the present invention can offer the lithium secondary cell a highenergy density, excellent charge and discharge cycle characteristics,and high stability.

[0073] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

What is claimed is:
 1. A method of producing a negative electrode for alithium secondary cell having a thin film made of an inorganic solidelectrolyte, comprising the steps of: placing, a closed containercontaining a negative electrode base material and a closed containercontaining a source material for an inorganic solid electrolyte, into achamber space, which is substantially inactive to lithium and which isinsulated from air and provided adjacent to an apparatus for formingsaid thin film, said base material having a surface made of a materialselected from the group consisting of lithium metal and lithium alloys;taking out said base material and said source material from eachcontainer in said chamber space; transferring said base material andsaid source material into said apparatus without exposing them to air;using said source material and forming a thin film made of an inorganicsolid electrolyte on said base material in said apparatus; transferringsaid base material having said thin film formed thereon,without exposingit to air, from said apparatus into a chamber space, which issubstantially inactive to lithium and which is insulated from air andprovided adjacent to said apparatus; and placing said base material intoa closed container in said chamber space.
 2. The method according toclaim 1, wherein said negative electrode base material is preparedthrough the process of forming a thin film made of a material selectedfrom the group consisting of lithium metal and lithium alloys on a basematerial by a vapor deposition method.
 3. The method according to claim2, wherein said thin film made of a material selected from the groupconsisting of lithium metal and lithium alloys has a thickness of atmost 20 μm.
 4. A method of producing a negative electrode for a lithiumsecondary cell having a thin film made of an inorganic solidelectrolyte, comprising the steps of: placing, a closed containercontaining a first source material and a closed container containing asecond source material, into a chamber space, which is substantiallyinactive to lithium and which is insulated from air and providedadjacent to an apparatus for forming said thin film, said first sourcematerial being selected from the group consisting of lithium metal andlithium alloys, and said second source material being for use in formingan inorganic solid electrolyte; taking out said first source materialand said second source material from each container in said chamberspace; transferring said first source material and said second sourcematerial into said apparatus without exposing them to air; using saidfirst and second source materials and forming a first thin film made ofsaid first source material and a second thin film made of said secondsource material on a base material in said apparatus; and transferringsaid base material having said first and second thin films formedthereon, without exposing it to air, from said apparatus into a chamberspace, which is substantially inactive to lithium and which is insulatedfrom air and provided adjacent to said apparatus; and placing said basematerial into a closed container in said chamber space.
 5. The methodaccording to claim 4, wherein said first thin film is formed by a vapordeposition method.
 6. The method according to claim 5, wherein saidfirst thin film has a thickness of at most 20 μm.
 7. A method ofproducing a negative electrode for a lithium secondary cell having athin film made of an inorganic solid electrolyte, comprising the stepsof: placing a closed container containing a first source material into achamber space, which is substantially inactive to lithium and which isinsulated from air and provided adjacent to a first apparatus forforming a thin film, said first source material being selected from thegroup consisting of lithium metal and lithium alloys; taking out saidfirst source material from said container in said chamber space;transferring said first source material into said first apparatuswithout exposing it to air; using said first source material and forminga first thin film made of said first source material on a base materialin said first apparatus; transferring the base material having saidfirst thin film formed thereon, without exposing it to air, from saidfirst apparatus into a chamber space, which is substantially inactive tolithium and which is insulated from air and provided adjacent to saidfirst apparatus; placing the base material having said first thin filminto a closed container in said chamber space; placing, said closedcontainer containing the base material having said first thin film and aclosed container containing a second source material, into a chamberspace, which is substantially inactive to lithium and which is insulatedfrom air and provided adjacent to a second apparatus for forming a thinfilm, said second source material being for use in forming an inorganicsolid electrolyte; taking out the base material having said first thinfilm and said second source material from each container in said chamberspace; transferring the base material having said first thin film andsaid second source material into said second apparatus without exposingthem to air; using said second source material and forming a second thinfilm made of said second source material on said first thin film in saidsecond apparatus; transferring said base material having said first andsecond thin films, without exposing it to air, from said secondapparatus into a chamber space, which is substantially inactive tolithium and which is insulated from air and provided adjacent to saidsecond apparatus; and placing said base material into a closed containerin said chamber space.
 8. The method according to claim 7, wherein saidfirst thin film is formed by a vapor deposition method.
 9. The methodaccording to claim 8, wherein said first thin film has a thickness of atmost 20 μm.
 10. The method according to claim 1, wherein, when saidsource material is taken out and transferred into said apparatus, saidchamber and said apparatus are filled with a gas selected from the groupconsisting of helium, nitrogen, neon, argon, krypton, a mixture gas oftwo or more from the foregoing, and dry air having a dew point of −50°C. or below.
 11. The method according to claim 4, wherein, when saidsource material is taken out and transferred into said apparatus, saidchamber and said apparatus are filled with a gas selected from the groupconsisting of helium, nitrogen, neon, argon, krypton, a mixture gas oftwo or more from the foregoing, and dry air having a dew point of −50°C. or below.
 12. The method according to claim 7, wherein, when saidsource material is taken out and transferred into said apparatus, saidchamber and said apparatus are filled with a gas selected from the groupconsisting of helium, nitrogen, neon, argon, krypton, a mixture gas oftwo or more from the foregoing, and dry air having a dew point of −50°C. or below.
 13. The method according to claim 1, wherein, when the basematerial having said thin film formed thereon is transferred from saidapparatus into said chamber and placed into said closed container, saidchamber and said apparatus are filled with a gas selected from the groupconsisting of helium, nitrogen, neon, argon, krypton, a mixture gas oftwo or more from the foregoing, and dry air having a dew point of −50°C. or below.
 14. The method according to claim 4, wherein, when the basematerial having said thin film formed thereon is transferred from saidapparatus into said chamber and placed into said closed container, saidchamber and said apparatus are filled with a gas selected from the groupconsisting of helium, nitrogen, neon, argon, krypton, a mixture gas oftwo or more from the foregoing, and dry air having a dew point of −50°C. or below.
 15. The method according to claim 7, wherein, when the basematerial having said thin film formed thereon is transferred from saidapparatus into said chamber and placed into said closed container, saidchamber and said apparatus are filled with a gas selected from the groupconsisting of helium, nitrogen, neon, argon, krypton, a mixture gas oftwo or more from the foregoing, and dry air having a dew point of −50°C. or below.
 16. The method according to claim 1, wherein said thin filmmade of said inorganic solid electrolyte contains components A to C inthe following: A: lithium, the content of which is in the range of 30%to 65% by atomic percent; B: one or more elements selected from thegroup consisting of phosphorus, silicon, boron, germanium, and gallium;and C: sulfur.
 17. The method according to claim 16, wherein said thinfilm made of said inorganic solid electrolyte further contains at leastone of oxygen and nitrogen.
 18. The method according to claim 16,wherein said thin film made of said inorganic solid electrolyte isamorphous.
 19. The method according to claim 16, wherein said thin filmmade of said inorganic solid electrolyte has an ionic conductance of atleast 1×10⁻⁴ S/cm at 25° C.
 20. The method according to claim 16,wherein said thin film made of said inorganic solid electrolyte isformed by any one method selected from the group consisting ofsputtering, vapor evaporation, laser ablation, and ion plating.
 21. Themethod according to claim 4, wherein said thin film made of saidinorganic solid electrolyte contains components A to C in the following:A: lithium, the content of which is in the range of 30% to 65% by atomicpercent; B: one or more elements selected from the group consisting ofphosphorus, silicon, boron, germanium, and gallium; and C: sulfur. 22.The method according to claim 21, wherein said thin film made of saidinorganic solid electrolyte further contains at least one of oxygen andnitrogen.
 23. The method according to claim 21, wherein said thin filmmade of said inorganic solid electrolyte is amorphous.
 24. The methodaccording to claim 21, wherein said thin film made of said inorganicsolid electrolyte has an ionic conductance of at least 1×10⁻⁴ S/cm at25° C.
 25. The method according to claim 21, wherein said thin film madeof said inorganic solid electrolyte is formed by any one method selectedfrom the group consisting of sputtering, vapor evaporation, laserablation, and ion plating.
 26. The method according to claim 7, whereinsaid thin film made of said inorganic solid electrolyte containscomponents A to C in the following: A: lithium, the content of which isin the range of 30% to 65% by atomic percent; B: one or more elementsselected from the group consisting of phosphorus, silicon, boron,germanium, and gallium; and C: sulfur.
 27. The method according to claim26, wherein said thin film made of said inorganic solid electrolytefurther contains at least one of oxygen and nitrogen.
 28. The methodaccording to claim 26, wherein said thin film made of said inorganicsolid electrolyte is amorphous.
 29. The method according to claim 26,wherein said thin film made of said inorganic solid electrolyte has anionic conductance of at least 1×10⁻⁴ S/cm at 25° C.
 30. The methodaccording to claim 26, wherein said thin film made of said inorganicsolid electrolyte is formed by any one method selected from the groupconsisting of sputtering, vapor evaporation, laser ablation, and ionplating.